1. Field of the Invention
This invention relates to a system for detecting or discriminating malfunction of an internal combustion engine radiator, more particularly to a system for detecting or discriminating malfunction of a thermostat in a cooling system of an internal combustion engine.
2. Description of the Related Art
The internal combustion engine of a vehicle is connected through a communicating passage with a radiator for cooling a coolant. A thermostat (a shut-off valve) is installed in the communicating passage. The thermostat closes the communicating passage when the coolant temperature is low, such as at engine starting, and opens it when the temperature rises so as to pass coolant into the radiator for cooling.
The radiator is one of the on-board components of a vehicle. The ability to detect or discriminate radiator malfunction is therefore desirable. For example, Japanese Laid-open Patent Application No. Hei 6(1994)-213117, which relates to a radiator equipped with a thermally insulated tank for storing coolant heated during ordinary operation, teaches a system that detects the coolant temperature at engine starting and determines that the thermally insulated tank is out of order when the detected temperature is abnormally low.
This earlier system can also determine when the thermostat is stuck closed or stuck open based on abnormally high or low detected coolant temperature during normal engine operation.
However, the ability of this conventional system to detect thermostat malfunction is limited to times when the detected coolant temperature is abnormal. It therefore does not provide satisfactory detection accuracy and response.